Problem: Express your answer as a mixed number simplified to lowest terms. $3\dfrac{1}{7}-1\dfrac{7}{8} = {?}$
Explanation: Find a common denominator for the fractions: $= {3\dfrac{8}{56}}-{1\dfrac{49}{56}}$ Convert ${3\dfrac{8}{56}}$ to ${2 + \dfrac{56}{56} + \dfrac{8}{56}}$ So the problem becomes: ${2\dfrac{64}{56}}-{1\dfrac{49}{56}}$ Separate the whole numbers from the fractional parts: $= {2} + {\dfrac{64}{56}} - {1} - {\dfrac{49}{56}}$ Bring the whole numbers together and the fractions together: $= {2} - {1} + {\dfrac{64}{56}} - {\dfrac{49}{56}}$ Subtract the whole numbers: $=1 + {\dfrac{64}{56}} - {\dfrac{49}{56}}$ Subtract the fractions: $= 1+\dfrac{15}{56}$ Combine the whole and fractional parts into a mixed number: $= 1\dfrac{15}{56}$